CSC 308 Requirements Engineering

Requirements Cont. • Introduction: Synchronization – where are we now

• Data-flow Diagrams • Entity-Relationship Diagrams

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CSC 308 Requirements Engineering

Synchronization • Note text chapters and other assigned readings – keep up with readings and journals – check the syllabus on line for further information

• Will assign each manager (or designate) a presentation at some point soon. – status report to class – evaluation of strengths/weaknesses of group structure ¤ and management style

– recommendation for improvement ¤ class input to be recorded

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CSC 308 Requirements Engineering

Next week • Groups to produce a Requirements document from the template – carefully track TBD’s ¤ assign responsibilities and schedule resolutions

– refine the V & S and the Risk Document as you go – focus on Use Cases for User Requirements ¤ moves us towards Functional requirements

– I suggest finding good examples of Requirements

documents

¤ besides those on my site

• Continue to elicit requirements (use cases and DD) – customer (and other stakeholder) contact

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CSC 308 Requirements Engineering

Suggestions (for good / passing grades) • Subordinate “student” vs. “professional” attitude – fulfillment of a goal you define – a “minimal” satisfaction of stated guidelines is not good – passing grades mean ability to add value to the team effort through

processes we discuss in class

¤ as has been said, easy to fail by flaking on the team, leading the team

astray ¤ crashing and burning project not necessarily failure at all ¤ team individual evaluations next week

• Check my 308 page for standards – pay close attention to each item, discuss relevance – look all around, follow links, figure out what is there!

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CSC 308 Requirements Engineering

Specific pointers • Date ALL documents • Author ALL documents • Assign responsibilities and schedule followups – enforce responsibility – can be lenient and trade off favors, but not one-sided! – journals contain action items and meeting notes

• Re-read and implement strategies discussed in class and in the book – how many groups have used the customer bill of rights

and responsibilities?

¤ is your customer a bit flakey? ¤ can you work with that to YOUR advantage? 5

CSC 308 Requirements Engineering

More • Prioritize everything (like scheduling!) – internal jobs, requirements, etc.

• Have a rich glossary of terminology • Build and maintain the data dictionary – all nouns in your use-cases are suspect – boldface all items in your data dictionary (at least for a consistency

check!)

• Use “test balloons” for the customer – – – – –

draw diagrams, suggest scenarios get their attention and keep them interested review and implement team building strategies if needed outside social events, stupid games, etc! See Ludi, Brooks, Yourdon (Death March) and others

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CSC 308 Requirements Engineering

Even More • Review Schach Chapters, Wiegers Chapter 10 • Pay attention to document QA! – team (testing at this stage of the lifecycle)- Document: ¤ sanity check ¤ English language usage, clarity of language ¤ clarity of concepts (or clarity of questions about concepts)

• Questions for your user/client/champion – – – – –

consider who you address do the questions make clear sense to the recipient? does the question maximize my information “take”? do my question appear professional? am I keeping my customer interested and confident? 7

CSC 308 Requirements Engineering

More yet again • Thoughts on Use-Cases – review the text, search around, look at examples – what are “use-cases” anyway? Really? – consider the following qualities ¤ traceability (consistency of usage) ¤ data items (dictionary entries) ¤ glossary terms ¤ use-case table of contents ¤ list of actors, roles, explanation in introduction ¤ descriptions of use-cases: simple, sequential, functional ¤ course of events: model the description graphically

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CSC 308 Requirements Engineering

Requirements Analysis and Specification

Vision and Scope

Use Case Document

Requirements Specification

informal statement of customer’s need for system

statement of what users need from system to perform needed tasks

notational and/or formal description of the software system

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CSC 308 Requirements Engineering

Purposes for Requirements • A medium for communication – between users, developers, coders, testers, managers,

marketeers and more – must be understandable, answer all relevant questions unambiguously

• A contract – to prevent (and settle) disputes – most common practice: no requirements and “contract” is

then expensive to determine

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CSC 308 Requirements Engineering

Requirements Analysis continued • How to facilitate a communications medium? – multiple views ¤ DFD ¤ ERD ¤ STD ¤ lots more... UML uses all these “old” concepts

– careful of the tradeoffs: always the cost/benefit analysis

to more views – some views more suited to certain kinds of projects ¤ process oriented (transaction systems) - DFD’s ¤ real time systems - STD’s ¤ database systems - ERD’s

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CSC 308 Requirements Engineering

• Best practice: some combination of views to complement carefully crafted textual requirements – UML is an attempt to help us learn this lesson ¤ did OMT do it as well?

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CSC 308 Requirements Engineering

Data-Flow Diagrams • Captures a system’s “logical” data flow – Emphasis is on “what” not “how” ¤ Logical: “Records” flow from database to application ¤ Implementation: “Records” are passed via remote procedure call • which in turn uses a network protocol called TCP/IP

– Developed using “stepwise refinement“

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CSC 308 Requirements Engineering

Stepwise Refinement – Stepwise Refinement is a problem-solving technique – Postpone (requirements/design) decisions on details until

as late as possible – Focus instead on the most important issues – Miller’s Law: 7±2 chunks

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CSC 308 Requirements Engineering

Data Flow Diagram Parts

DOUBLE SQUARE

arrow rounded rectangle

OPEN-ENDED RECTANGLE

Source or destination of data

Flow of data Process which transforms a flow of data (note, Wie. uses a circle) Store of data

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CSC 308 Requirements Engineering

Simple Example • Sally’s software shop – small shop, buys and resells software at retail – sells from stock and makes orders – extends credit to inst., corps and some indiv. – monthly turnover of 300 packages / $250 each

• Sally says she wants to computerize – you ask “why”? – what is her goal? ¤ to make more money? • more efficiency • better customer service 16

CSC 308 Requirements Engineering

Sally’s Software Shop (cont’d) ¤ to hide assets from her ex-husband with 9 kids?

• Do we usually just say “sure” and begin design? – find out what the real problem is later...

• Investigate client’s needs first. – DFD’s, in addition to use cases help define the problem

• Overall steps (we cover the first): – Draw DFD, stepwise refinement – Decide what sections to computerize and how (batch or

online) – Put in details of the data flows – Define the logic of the proceses 17

CSC 308 Requirements Engineering

Sally’s Software Shop (cont’d) • • • • •

Define the Data Stores Define the Physical Resources Determine the Input/ Output Specifications Perform Sizing Determine the Hardware Requirements

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CSC 308 Requirements Engineering

First Step (a context diagram with data stores) Here are the major players; details on data deferred PACKAGE DATA

package details

CUSTOMER

order invoice

process orders credit status CUSTOMER DATA

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CSC 308 Requirements Engineering

Second Refinement PACKAGE DATA SOFTWARE SUPPLIER

package details CUSTOMER

order

verify order details of package to be ordered is valid credit status CUSTOMER DATA

invoice

assemble orders

addr. or tel.

place order with supplier

batched order PENDING ORDERS

details of package on hand

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CSC 308 Requirements Engineering

(part of) Third Refinement PACKAGE DATA

package details CUSTOMER

order

details of package to be ordered

verify order is valid credit status

details of package on hand

CUSTOMER DATA

pmnt

delivery note

address

assemble orders

details of package received from software supplier

delivery details invoice

apply payment pmnt details

create invoice

invoice details

ACCT’s RECEIVABLE 21

CSC 308 Requirements Engineering

Data-Flow Diagram Wrap-Up • We could easily continue with our example! • Determining when to stop depends on your task – For requirements, this is a good start – For design, we would want to continue on

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CSC 308 Requirements Engineering

Entity-Relationship Diagrams • Used to specify relationships between entities in the system – These relationships can lend insight into the requirements

and/or design of a system

• Originally used in the database domain; now being used in Object-Oriented Analysis

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CSC 308 Requirements Engineering

Entity-Relationship Diagram Parts

Entity

Some object of the system (look at the Data Dictionary)

1

1

one-to-one relationship

1

n

one-to-many relationship

n

m

many-to-many relationship

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CSC 308 Requirements Engineering

One-to-One Relationships

United States

California

CSC 205

1

1

1

1

1

1

President

Los Angeles

Instructor

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CSC 308 Requirements Engineering

One-to-Many Relationships

Author

California

CSC 205

1

writes

n

1

n

1

n

Book

City

Student

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CSC 308 Requirements Engineering

Many-to-Many Relationships

Child

n

2

Parent

n tournament n Tennis Player Tennis Player round

Class

m

n

Student

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CSC 308 Requirements Engineering

Observations • Each entity has a name and is singular – e.g. “Book” not “Books”, the relationship specifies the

number

• Each relationship has a point-of-view, a context, and an optional name. – The name helps to establish the context

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CSC 308 Requirements Engineering

Example

Supplier m

to use in p

is supplied by

Project

n

Part 1

n

consists of 29

CSC 308 Requirements Engineering

Additional Observations • An Entity can have relationships with other instances of itself – e.g. a part can consist of other parts

• n-ary relationships between entities can be established

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CSC 308 Requirements Engineering

Simple Example • A user creates many webpages each of which contain many links to other webpages. These webpages are all located on a particular website.

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CSC 308 Requirements Engineering

Example Diagram

User 1

creates n n

Webpage 1

1

Website

n

links to

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CSC 308 Requirements Engineering

State Transition Diagram (STD)

First System State

condition 3; outcome 3

condition 1; outcome 1 condition 2; outcome 2

Second system state

Third System State condition 4; outcome 4

Models the discrete states a system can be in (state?) Transitions show the only permitted state changes Can also model possible status of an object in the system 33

CSC 308 Requirements Engineering

UI model using a dialog map Enter System

Exit System

cancel

Send note

Next menu

Send a Feedback note

Main Menu Page 1

Previous Menu

Main Menu Page 2

select feedback

Return to menu

select file operations

Delete File rename file

File Options Menu

Cancel

Cancel Select Rename

Rename a File Dialog

Select Cancel

Delete a File Dialog 34

CSC 308 Requirements Engineering

Benefits of a dialog map • • • • • •

Find incorrect or missing transitions early Find missing or incorrect requirements early Spot opportunities for reuse Spot redundancies in UI design Can partition the UI into sub components Can do state transition diagrams hierarchically, to control the scope of the views

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CSC 308 Requirements Engineering

Requirements plus Test Cases plus Dialog Maps • Requirement: If the stockroom contains smaples of the chemical being ordered, the system shall display a list of the available samples. The user wshall either select a sample, or request to place a new order from the vendor. • Test Case: At DB40, enter a valid chemical ID with 2 samples in the stockroom. DB50 appears, with the 2 sample numbers. Select sample 2. DB50 closes and sample 2 is added to the bottom of the current chemical request list in DB70.

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CSC 308 Requirements Engineering

Dialog Map for Chemical Example

cancel

DB40: select chemical to order

chemical ID OK stockroom has sample

cancel

chemical ID OK no sample in stockroom

order new bottle DB50: Stockroom Sample List

DB60: list of vendors for chemical

sample selected OK

vendor selected OK DB70: current chemical request list

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